Origin.—Several theories as to the ori gin of coal have been put forth from time to time. The one now generally re ceived is that the rank and luxuriant vegetation which prevailed during the Carboniferous Period grew and decayed upon land raised but slightly above the sea; that by slow subsidence this thick layer of vegetable matter sank below the water and became gradually covered with sand, mud, and other mineral sedi ment; that then, by some slight up heaval of the sea-bottom or other process, a land surface was once more formed and covered with a dense mass of plants, which in course of time decayed, sank, and became overlaid with silt and sand as before. At length thick masses of stratified matter would accumulate, pro ducing great pressure, and this, acting with chemical changes, would gradually mineralize the vegetable layers into Coal. Some experiments made by Dr. Lindley a few years ago showed that of a large number of plants kept immersed in water for two years, the ferns, lycopodiums, and pines were those which had the greatest powers of resisting decay, and Coal appears to be mainly composed of the substance of the ancient gigantic representatives of these three orders of plants. The interesting fact has also been lately proved by Huxley, Morris, Carruthers, and others, that in many in stances the bituminous matter in Coal is formed almost wholly of the spore cases and spores of plants allied to our club mosses and ferns.
Sources of Supply.—Since the pros perity of great national industries, as well as much of our domestic comfort, depends on the continuance of an abun dant and cheap supply of fuel, much anxiety has arisen of late years regard ing the future supply and price of Coal. An exhaustive survey of the Coal fields of the world has produced the estimate that there exist in the United States and Alaska, 4,231,000,000,000 tons, of which 22,000,000,000 tons is anthracite, 2,155, 000,000,000 tons is bituminous, and 2, 054,000,000,000 tons is sub-bituminous and lignite; Canada, 1,361,000,000,000 tons, of which 2,000,000,000 is anthracite and 313,000,000,000 is bituminous; China, 1,097,000,000,000 tons, of which 427,000, 000,000 is anthracite; Germany, 467,000, 000,000 tons, of which 452,000,000,000 tons is bituminous and the rest sub bituminous; Great Britain, 209,000,000, 000 tons, of which 12,000,000,000 is an thracite; Siberia, 192,000,000,000 tons, no anthracite; Australia, 183,000,000,000 tons, all bituminous or sub-bituminous; India, 87,000,000,000 tons, no anthracite • Russia in Europe, 66,000,000,000 tons, of which 41,900,000 is anthracite; Union of South Africa, 62,000,000,000 tons, of which 13,000,000,000 is anthracite; Aus tria, 59,000,000,000 tons, no anthracite; Colombia, 30,000,000,000 tons, no anthra cite; Indo-China, 22,000,000,000 tons, all anthracite; France, 19,000,000,000 tons, of which 4,000,000,000 is anthracite; Belgium, 12,000,000,000 tons, no anthra cite; Spain, 10,000,000,000 tons, of which 2,000,000,000 is anthracite; Spitzbergen, 9,000,000,000 tons, no anthracite; Japan, 9,000,000,000 tons, no anthracite; Hol land, 5,000,000,000 tons, no anthracite; other countries, 24,000,000,000 tons, of which 3,000,000,000 is anthracite.
Total Coal reserves, 8,154,000,000,000 tons, of which 548,000,000,000 is an thracite; 4,302,000,000,000 is bituminous, and 3,304,000,000,000 is sub-bituminous and lignite.
Coal in the United States.—The entire area of these is about 330,000 square miles. The principal fields are (1) Eastern, approximately 70,000 square miles; (2) the Interior area, about 133, 000 square miles; (3) the Gulf area, 3—Vol. III—Cyc about 2,100 square miles; (4) the North ern or Great Plains area, about 88,000 square miles; (5) the Rocky Mountain area, about 37,000 square miles; (6) and (7) Pacific Coast area, about 1,900 square miles.
Anthracite Area s. — Commercially speaking, the anthracite division may be said to consist of Pennsylvania alone, although a small amount of anthracite coal is mined in other States. The orig inal Coal beds of New England have been metamorphosed into graphite and graphitic Coal. This area is confined to eastern Rhode Island, and the counties of Bristol and Plymouth, Mass. The prod
uct mined from the beds, which may be more properly called graphite than Coal, requires a considerable degree of heat Northern or Wyoming and Lackawanna, mostly in Luzerne and Lackawanna cos. (5) The Loyalsock and Mehoopany field is within the area drained by the head waters of two creeks of that name, 20 or 25 miles N. W. of the W. end of the field last mentioned. The anthracite region of Pennsylvania, as a whole, has a maximum length of about 115 miles, a maximum breadth of about 40 miles; area about 1,700 square miles; but the area underlaid by workable Coal beds is only about 470 square miles.
Bituminous Areas.—The bituminous Coal areas of the United States may for convenience be grouped into seven di visions: the Triassic, the Appalachian, the Northern, the Central, the Western, the Rocky Mountain, and the Pacific for combustion, and can be used only with other combustible material or under an intense draught or blast. Its prin cipal use is in the direct manufacture of steel; the entire annual output is but a few thousand tons. There are five recog nized principal divisions of the Pennsylva nia anthracite region: (1) The Southern or Pottsville field, extending from the Lehigh river, at Mauch Chunk, S. E. to within a few miles of the Susquehanna river, directly W. of Harrisburg. (2) The Western Middle or Mahanoy and Shamokin field, extending from the east ernmost headwaters of the Little Schuyl kill river to the Susquehanna. These are sometimes grouped together and given the common name of the Schuyl kill region. (3) The Eastern Middle or upper Lehigh field, lying between the Lehigh river and Catawissa creek, and mostly situated in Luzerne co. (4) The Coast areas. The eastern Triassic area is composed chiefly of the Richmond basin, in Virginia, and the Deep River and the Dan River fields, in North Caro lina. No extensive mining operations are now carried on in this area. The Appalachian field is immediately W. of the E. border of the Appalachian range, and extends from New York on the N. to Alabama on the S., its direction being N. E. and S. W.; length, about 900 miles; width, from 30 to 180 miles. There are in this region many varieties of bituminous Coal, the best and most productive beds on the whole being those of the Pittsburgh district and of West Virginia. The thickness of the coal measures in different sections varies from 100 to over 3,000 feet. The north ern bituminous area is all in central Michigan. The coal here found is not of superior quality, and is used mostly for local supply. Of the central area three-fourths are in Illinois, less than one-sixth in Indiana, and about one twelfth in western Kentucky. In the western field the most extensive mining operations have been carried on in Iowa and Missouri; its area is greater than that of any other one Coal field in the United States. The coals are of great variety; the best which has so far been mined is that of the Indian Territory. The Rocky Mountain Coal beds have have been found in the geological forma tions from the Carboniferous up to and including the Cretaceous, differing in this respect from those hitherto enumer ated, which, with the exception of that in Virginia and North Carolina, are all con was not largely employed until the 18th century. Of late years rock-drills driven by steam or by compressed air have come largely into use. The bore-hole, when finished, is then charged. The gunpow der is inclosed in a little bag of cloth dipped in pitch and provided with a fuse. The fullest benefit of modern explosives, such as dynamite, gun-cotton and yonite, can be obtained only by the use of strong detonators fired by electricity, by which it is impossible to place a number of bore-holes in such a manner that when fired simultaneously they shall help one another. Blasting powder is still used for removing coal and millions of tons are obtained by its aid. In order to obvi ate the danger of explosions in fiery col fined to the Carboniferous. Coal has been mined in the Pacific States.